This invention relates to a gas turbine engine including a gas turbine gas generator and a separate power turbine driven by the gas generator for use in a process of converting heat energy released by fuel combustion into mechanical energy and, more particularly, to an apparatus for controlling the energy conversion function of the gas turbine engine to permit the engine to run without engine surge.
Gas turbine engines have been used in automotive vehicles for converting heat energy released by the combustion of fuel into mechanical energy. One serious problem which exists with such gas turbine engines, particularly with two-axle gas turbine engines, is that engine surge occurs with noise and vibration upon the simultaneous occurrence of two conditions; namely, when the amount of air flow through the compressor is within a particular range and when the ratio of pressures at the inlet and outlet of the compressor is within a particular range. Under a surge condition, the gas turbine engine does not run in the most efficient manner and sometimes ceases to run at all. To obtain the maximum performance from a gas turbine engine, however, it is desirable to run the engine quite close to its surge level. Thus, the need exists for a practical approach which overcomes this dilemma by controlling the engine as close to its surge level as possible while avoiding engine surge.
In order to avoid engine surge, it has been attempted to limit values calculated from sensed engine operating conditions for setting a device used to control the energy conversion function of the engine within a predetermined range. With such attempts, however, it is required to provide a large margin at the limitation range so as to avoid engine surge over the entire mode of engine operation, at the sacrifice of acceleration performance and other engine performances. In addition, because of engine characteristic changes with the passage of time and clogging of the engine air passage, the margin determined upon designing the engine will be insufficient to avoid engine surge over the entire engine operation range.
Another problem occurs with gas turbine engines having a closed loop system for feedback control of the speed of rotation of the gas generator. The gas generator speed tends to decrease when engine surge exists. Under a surge condition, the closed loop system will attempt to correct the gas generator speed by supplying more fuel to the engine, causing the engine surge to be accelerated.
Therefore, the present invention provides a gas turbine control apparatus which permits a gas turbine engine to run quite close to its surge level while avoiding engine surge, thereby achieving high engine efficiency and high acceleration performance without degrading driving feel.